The present invention relates generally to a device for treating a blockage or stenosis in a vessel of a patient and a method for making the device. More specifically, the present invention relates to a balloon for a dilation catheter that is useful for performing medical dilation procedures such as angioplasty, and/or delivering a stent and a method for manufacturing the balloon.
It is well known that many medical complications are caused by a partial or total blockage or stenosis of a blood vessel in a patient. Depending on the location of the stenosis, the patient can experience cardiac arrest, stroke, or necrosis of tissues or organs.
Several procedures have been developed to treat stenoses, including angioplasty, incising and dilating the vessel, and stenting. These procedures typically utilize a dilation catheter having a balloon to dilate the vessel or deliver the stent. The desired size and physical characteristics of the balloon depend largely upon the size of the vessel and the intended use of the balloon.
Generally, balloons for dilation catheters are classified according to their xe2x80x9ccompliancexe2x80x9d or expandability relative to other balloons. Typically, a balloon is rated as being either xe2x80x9ccompliant,xe2x80x9d xe2x80x9csemi-compliant,xe2x80x9d or xe2x80x9cnon-compliant.xe2x80x9d A comprehensive definition of these terms is provided in U.S. Pat. No. 5,556,383, issued to Wang et al. and entitled xe2x80x9cBlock Copolymer Elastomer Catheter Balloons,xe2x80x9d the contents of which are incorporated herein by reference.
The physical characteristics of the balloon are primarily influenced by how the balloon is formed and by the material utilized in the balloon. Presently, most balloons are formed from a tube which is heated to above its glass transition temperature and radially expanded in a blow mold. Often, the tube is also subjected to an axial stretch so that the resulting balloon is bi-axially oriented.
Typically, non-compliant balloons are made from materials, such as polyethylene terephthalate. These non-compliant balloons are often relatively inflexible, are prone to develop pin holes, and the balloon does not rewrap well after inflation in the vessel. As a result thereof, these balloons are often difficult to remove from the delivery catheter. Further, if these balloons are used to position a stent in the vessel, the balloon frequently catches on the stent and repositions the stent in the vessel. On the other extreme, compliant balloons are typically made of materials, such as polyvinyl chlorides. However, compliant balloons often have a relatively low tensile strength, do not expand in a predictable fashion, and are subject to rupture during high pressure applications.
Recently, a number of semi-compliant balloons have been manufactured using materials, such as nylon and polyamide-polyether copolymers. These balloons exhibit many desirable characteristics including relatively thin walls, a soft texture, a low uninflated crossing profile, thermal stability, and good tensile strength. However, present semi-compliant balloons are not completely satisfactory, since these semi-compliant balloons are made by standard blow molding processes. For example, the wall thickness of a balloon manufactured by standard processes may be inconsistent and/or the balloon may have a compliance curve which is too steep or too flat. This can lead to unpredictable balloon inflation and/or over-inflation of the balloon in the vessel.
Further, it has been discovered that certain polymers, which exhibit desirable physical properties, can not be formed into a balloon using the present blow molding processes. In fact, these materials, namely certain polyester block copolymers will rupture during a typical blow molding process. Thus, it is believed that these polyester block copolymers have not been used for balloons.
In light of the above, it is an object of the present invention to provide a -balloon having improved physical characteristics for a wide variety of applications. It is another object of the present invention to provide a balloon having relatively thin, consistent walls, a soft texture, and a low uninflated crossing profile and a low rewrap profile after inflation in the vessel. Another object of the present invention is to provide a balloon which is thermally stable, semi-compliant, expands in a predictable fashion, and has improved tensile strength. Still another object of the present invention is to provide a balloon made from certain polyester block copolymers. Yet another object of the present invention is to provide a simple method for manufacturing a balloon which has greater control over the physical properties of the balloon.
The present invention is directed to a balloon for a dilation catheter and a method for manufacturing a balloon which satisfy these objectives. The method for forming the balloon includes the steps of providing a tube, positioning the tube in a precondition mold, preconditioning the tube within the precondition mold to form a parison, positioning the parison in a balloon mold, and expanding the parison within the balloon mold to form the balloon.
As provided in detail below, the unique use of the precondition mold to form the parison from the tube provides for greater control over the dimensions and properties of the balloon. Further, certain materials which could not be formed into a balloon using prior art blow molding processes can be formed into a balloon using the process provided by the present invention.
As used herein, the term xe2x80x9cparisonxe2x80x9d means and describes the preform which results from preconditioning the tube in the precondition mold.
The step of preconditioning of the tube to form the parison typically includes radially expanding the tube within the precondition mold to form the parison. Radial expansion of the tube can be accomplished by heating the tube to a first temperature (xe2x80x9cT1xe2x80x9d) and pressurizing a lumen of the tube to a first pressure (xe2x80x9cP1xe2x80x9d). For the polyester-block copolymers provided herein, the first pressure P1 is at least approximately five hundred (500) psi.
The amount of preconditioning of the tube can vary according to the material utilized for the tube and the desired physical characteristics of the balloon. For example, the precondition mold can be sized so that the parison has a parison outer diameter which is at least over one (1) times larger than a tube outer diameter of the tube. Typically, however, the precondition mold is sized so that the tube radially expands within the preconditioning mold to form a parison having a parison outer diameter which is between approximately one and one-half (1.5) and two and one-half (2.5) times larger than the tube outer diameter. More specifically, for some of the embodiments provided herein, the precondition mold is sized so that the parison outer diameter is approximately one and seven-tenths (1.7) times larger than the tube outer diameter.
Preferably, the step of preconditioning of the tube to form the parison also includes axial stretching of the tube in the precondition mold. As provided herein, the tube can be axially stretched between approximately one and one-half (1.5) to two and one-half (2.5) an original tube length of the tube. This results in a highly oriented and work hardened parison which is ready to be formed into the balloon. Further, a wall thickness of the tube is substantially uniformly reduced within the precondition mold.
The balloon mold is typically sized so that parison can be radially expanded in the balloon mold to form a balloon having a balloon outer diameter which is between approximately one and one-half (1.5) and two and one-half (2.5) times larger than the parison outer diameter. More specifically, for some of the embodiments provided herein, the balloon mold is sized so that the parison is radially expanded into a balloon having a balloon outer diameter which is approximately two (2) times larger than the parison outer diameter.
Preferably, the parison is also axially stretched in the balloon mold so that the resulting balloon is highly bi-axially oriented. As provided herein, the parison can be axially stretched between approximately one (1.0) to one and one-half (1.5) times the parison length of the parison.
Additionally, it has been discovered that a balloon exhibiting superior physical characteristics, including a low crossing profile, a low rewrap profile, a soft texture, thermal stability, and semi-compliant expansion can be formed from polyester block copolymers. Specifically, it has been discovered that a superior balloon can be manufactured from a block copolymer which consists of an aromatic polyester hard segment and an aliphatic polyester soft segment. For example, an excellent balloon can be made from the copolymer sold under the trade name xe2x80x9cPelprene,xe2x80x9d by Toyobo, located in Osaka, Japan. This copolymer consists of an aromatic polyester hard segment and an aliphatic polyester soft segment. Additionally, it is believed that an excellent balloon can be made from the copolymer sold under the trade name xe2x80x9cHytrel,xe2x80x9d by DuPont, located in Wilmington, Del. This copolymer consists of a polybutylene terephthalate hard segment and a long chain of polyether glycol soft segment.
Importantly, the softening point for the specific polyester block copolymers identified above is very close to the melting point of the material. For these materials, little strength of the material is lost and little softening occurs during a standard blow mold process. With these materials, the pressure needed to initiate expansion of the tube is very high, typically, at least approximately five hundred (500) psi. With these polyester block copolymers, this would cause the tube to rupture prior to forming the balloon using a standard blow molding process. However, these materials can be formed into a balloon utilizing the unique process provided herein.
Additionally, the present invention relates to a device for manufacturing a balloon. The device includes a precondition mold suitable for expanding the tube into a parison and a balloon mold suitable for expanding the parison into a balloon.